1. Field of the Invention
The present invention relates to a safety guard suitable for use with wide angle joints as fitted to agricultural power takeoff shafts.
2. Background and Related Art
Worldwide standards dictate that agricultural power takeoff (PTO) shafts must be enclosed by an approved safety guard. A safety guard for a standard PTO is shown in my Australian patent number 2005202533 also published as U.S. Pat. No. 7,621,688), the entire contents of which are incorporated herein by cross-reference. Standard PTO guards typically comprise a hollow tube portion that fits over the PTO shaft and an enlarged portion at either end that fits over the end yokes of the PTO. Most standard PTO safety guards are also provided with a bellows at either end which extends further over the end joints of the PTO. The bellows are usually cylindrical or frusto-conical in shape and usually have a corrugated outer surface to allow for some bending in the bellows.
Standard agricultural PTO shafts incorporate universal joints that operate at angles of approximate 15 to 20°, with a maximum permitted angle of around 35°. Many modern trailed type PTO driven agricultural implements, such as sprayers and harvesting machines, require a PTO shaft with the ability to allow sharp turns by the tractor and the trailed implement. To meet this requirement, PTO shafts with wide angle joints (which allow rotation to wide angles, typically up to around 80°) are provided.
A typical construction for a wide angle PTO joint utilizes tandem Cardan type joints. Use of a double Cardan joint with an unsupported PTO shaft would result in the centre section of the shaft drooping and oscillating in an uncontrolled elliptical manner. To support and maintain axial alignment of the ends of the wide angle joint, a large diameter oscillating centre disc is incorporated. The centre of this disc engages with spigots provided on the adjacent joint end yokes. This disc slides in an elliptical manner within an outer disc housing.
The large diameter centre disc housing is provided with an outer bearing groove. This bearing groove is utilized to carry a bearing supporting the wide-angle portion of the PTO shaft safety guard, thus allowing the joints to rotate freely within the guard. The extreme operating angle of these joints dictates that the wide-angle portion of the guard (which overlies the wide-angle joint) must be carried on the joint itself.
Current agricultural safety guard requirements dictate that the tractor PTO shaft must be covered by a metal tractor master guard and that the implement PTO shaft must be guarded to a point close to the end of the implement shaft.
In use of present wide angle PTO joint safety guards, attempts to operate the implement PTO shaft attachment locking mechanism, which is typically obscured by the large diameter wide-angle shaft guard and the metal tractor guard, is extremely difficult and dangerous with heavy shafts located within the confines of the implement drive area.
The necessity to provide a wide-angle joint cover with a large outer diameter centre section to clear the joint centre disc housing while meeting the safety guard requirements of a small opening at the shaft attachment dictates that current full circle type guards cannot be slid back from the joint to facilitate shaft attachment.
Current versions of wide angle guards are generally attached by a number of screws or similar fasteners. This increases the time required to fit and remove the safety guard. Furthermore, even if the guard is dismantled, the small end diameter of the housing prevents access to the shaft end yoke.